There are many applications wherein arrays of optical elements are used for spectrally-selective processing of an optical beam, including optical spectrometry, optical performance monitoring, in wavelength blockers and wavelength switches. Depending on the application and a preferred technology, such arrays are typically formed by pixelated liquid crystal cells, multiple individually controlled micro-mirrors, or multiple photo-detectors such as CCD elements; they can be used to perform such operations as blocking or transmitting incident light based on its polarization, re-directing it in space, or converting it into electrical signals.
FIG. 1 shows a typical prior-art configuration, wherein a wavelength dispersed optical beam 102 impinges on a linear pixelated array 101 composed of rectangular optical elements 100 disposed along an axis. The optical beam is typically focused on the array and is dispersed in space along a so-called dispersion axis so that different optical elements of the array receive different spectral components of the beam, or different wavelengths. This configuration is used for example in wavelength blockers, dynamic gain equalizers and wavelength switches disclosed in U.S. Pat. No. 6,498,872 issued to Bouevitch, et. al, and in WDM switches disclosed in U.S. Pat. No. 6,707,959 issued to Ducellier, et al., both of which are assigned to the assignee of this application, and in many other commercially available optical devices and modules.
In many applications, it is important to accurately align the dispersed optical beam and the array, i.e. to align the axis of dispersion with the array axis. A problem of beam alignment arises in many optical systems, and multitude of beam alignment approaches exist in the prior art. For example, U.S. Pat. No. 4,071,754 issued to Roulund teaches a beam alignment detector comprised of a beam detector chip and an array of fiber optic ends orthogonal to the direction of laser beam scan. U.S. Pat. No. 6,792,185 to Ahrens, et al. discloses an optical structure for laser beam-fiber end alignment consisting of an optical bundle comprised of an array of optical fibers, arranged surrounding the receiving fiber.
Although the aforementioned inventions appear to perform their intended functions, they provide solutions requiring additional array structures that may significantly complicate the aforementioned WDM modules. While the task of finding efficient and cost-effective approaches to optical alignment requires solutions targeted to a specific system, these and other prior-art beam alignment methods are targeted to optical systems which are different from the one shown in FIG. 1.
It would be beneficial to the applications to have a relatively simple method of beam-array alignment in WDM modules and systems which wouldn't involve significant changes to the modules and would enable 1) an initial alignment of the beam to the array during assembly of the optical system, 2) monitoring drifts in the beam position through the manufacturing process, for instance, during packaging, and 3) monitoring drifts in the beam position over the life of the module, e.g. to assist in performance degradation diagnostics. However, to the best of our knowledge, heretofore there have been no simple approach to accurately measure the beam position and beam tilt relative to the array of rectangular elements without bringing at least a portion of the dispersed beam outside the array area, therefore strongly complicating alignment diagnostics for systems comprising pixel arrays for spectrally-selective processing of dispersed optical beams.
An object of this invention is to provide an array of optical elements for processing of a spatially dispersed beam of light with features enabling identification of the beam position in the array.
Another object of this invention is to provide an array of optical elements for processing of a spatially dispersed beam of light incorporating beam alignment features.
Another object of this invention is to provide a method for detecting of alignment of a dispersed beam of light relative to an array of beam-processing optical elements.